The present invention relates to colorless or near colorless compounds useful for marking or tagging petroleum fuels. It also pertains to a reagent useful in developing color of base-extractable markers. It also relates to a method for bleaching the color of the developed marker thereby restoring the fuel to its original appearance so that it may be combined with undeveloped marked fuel, avoiding the necessity of disposing separately of a potentially hazardous marker extract, which is customary in the prior art.
A marker is a substance which can be used to tag petroleum products for subsequent detection and is ordinarily colorless in the petroleum product. The marker is dissolved in a liquid to be identified, then subsequently detected by performing a simple physical or chemical test on the tagged liquid. Markers are sometimes required by government to ensure that the appropriate tax has been paid on particular grades of fuel. Oil companies also mark their products to help identify those who have diluted or altered their products. These companies often go to great expense to make sure their branded petroleum products meet certain specifications, for example, volatility and octane number, as well as to provide their petroleum products with effective additive packages containing detergents and other components. Consumers rely upon the product names and quality designations to assure that the product being purchased is the quality desired.
It is possible for unscrupulous gasoline dealers to increase profits by selling an inferior product at the price consumers are willing to pay for a high quality branded or designated product. Higher profits can also be made simply by diluting the branded product with an inferior product. Policing dealers who substitute one product for another or blend branded products with inferior products is difficult in the case of gasoline because the blended products will qualitatively display the presence of each component in the branded products. The key additives made to the branded products are generally present in such low levels that quantitative analysis to detect dilution with an inferior product is very difficult, time consuming and expensive.
Marker systems for fuels and other petroleum products have been suggested but various drawbacks have existed which have hindered their effectiveness. Many, for instance, lose their effectiveness over time, making them too difficult to detect after prolonged storage. In addition, reagents used to develop the color of markers often are difficult to handle or present disposal problems. Furthermore, some marking agents partition into water. This causes the markers to lose effectiveness when storage occurs in tanks that contain some water. The fuels and other petroleum products are themselves substantially free of water.
The compositions of the present invention contain compounds conventionally described as hydroxyphthaleins. Some of these are well established as visual pH indicators in the field of laboratory acid/base titrimetry. Some have also been proposed as suitable for some biomedical applications, however their use as marker or tagging substances for Petroleum fuels and additives is unique.
A similar compound that has been considered for use as a marker is Phenolphthalein. Its use was proposed in 1994 as a fuel marker by the U.S. Environmental Protection Agency and subjected to an oil refinery field trial under their auspices. The trial was unsuccessful, because phenolphthalein lacks adequate solubility in petroleum fuels at the concentration required as a marker. This caused the phenolphthalein to partially crystallize from the fuel, resulting in undermarking and contamination of refinery equipment, pipelines, etc. Phenolphthalein is also significantly soluble in water and it partially extracted from the marked fuel into the water layer which frequently accumulates at the bottom of fuel storage tanks, thus rendering it useless as a quantitative fuel marker. Furthermore, phenolphthalein is particularly sensitive to the alkalinity of the extraction or development reagent. With an aqueous extractant having a pH of less than 10.5, extraction is slow and incomplete, however above about pH 11 phenolphthalein rapidly forms a colorless trianion. These defects do not apply to the substances of the current invention.
Markers of the present invention possess increased petroleum fuel solubility and decreased solubility in neutral water. Their susceptibility to trianion formation and partial decolorization of the colored dianion in the presence of strong bases is also minimized. These advantages appear to occur due to the presence of an alkyl or alkoxy group adjacent to the ionizable hydroxy group of the markers of this invention.
The present invention provides markers which are invisible in liquid petroleum products at an effective level of use but that provide a distinctive color when extracted from the petroleum product with an appropriate developing reagent. The reagents used to develop the color are themselves easy to use, handle and dispose of.
The fact that the markers of the present invention impart no visible color to petroleum fuels at an effective dosage level makes them suitable for marking a wide range of petroleum products. Currently, for instance, they may be useful for marking or tagging on-road, low sulfur, diesel fuel. A regulation issued by the Federal Government precludes the addition to such fuel of any dye or dye related substance that will impart visible color to the fuel at an effective treatment rate. This regulation prevents the use of variously intensely colored substances proposed in the prior art as petroleum fuel markers, for instance those disclosed in U.S. Pat. Nos. 5,156,653; 5,205,840; 4,764,474; and 4,735,631. The disclosures of each of these patents is incorporated herein by reference.